The month before you're back at work: Once you've hired a caregiver, create an agreement. It should outline what you each expect from the arrangement.
A couple of weeks before: Do a test run. It'll ease the transition -- and your mind! Invite the sitter over for an hour or so while you run to the grocery store, or drop your child off at day care for the afternoon.
The week before: Get gear together. Gather the items on the day-care center's checklist, pack them into a knapsack or tote, and put it by the door. If you're using a sitter, make sure your supplies are fully stocked. Running out for diapers and wipes the night before your first day at work: no fun.
A few days before: Start implementing your new morning routine. Consider who should shower first and who should feed and dress the baby -- and remember to build in an extra 10 minutes for surprises (think poop).
The first day at work: Quickly say goodbye to your child, then leave. Lingering will make separation harder for both of you. If you need to call five times, fine -- you're adjusting too.